Process and apparatus for producing high-bulk synthetic yarns



3,408,277 -BULK Oct. 29, 1968 J. c. MARTIN ETAL PROCESS AND APPARATUS FOR PRODUCING HIGH SYNTHETIC YARNS Filed Feb. 8, 1965 r h m 7 WT m W e d M -m C W n. J

/mr/eg Wqfl w $7M ka k/$5 V MZQ United States Patent 3,408,277 PROCESS AND APPARATUS FOR PRODUCING HIGH-BULK SYNTHETIC YARNS Jean Claude Martin, Lyon, Rhone, and Charles Martin, Lyon, France, assignors to Societe Rhodiaceta, Paris, France, a French body corporate Filed Feb. 8, 1965, Ser. No. 431,007 Claims priority, application France, Feb. 14, 1964, 963,851 11 Claims. (Cl. 264-168) ABSTRACT OF THE DISCLOSURE Spontaneously crimpable fibres comprising chemically identical polymers differing in physical shrinkage-affecting characteristics such as viscosity are obtained by a melt spinning process in which molten polymer from a single melting zone passes to the spinneret through two or more conduits of different lengths or differently heated, so that the two or more streams of melt undergo different thermal treatments which give them different physical properties. A suitable apparatus is also described.

This invention relates to a process and apparatus for preparing, by melt extrusion, spontaneously crimpable filaments from thermoplastic organic polymers, and in particular from polypropylene. It will be understood that the individual filaments can be, and frequently will be, obtained in the form of a multifilament yarn.

By spontaneous crimping is meant a crimping which results from the relief of internal stress in the filaments, and is not the consequence of mechanical deformation undergone by the filaments.

Synthetic filaments and fibers prepared by melt extrusion having a linear structure and a smooth surface which, on weaving or knitting, yield fiat articles whose appearance and handle are not always suitable for some applications in which, nevertheless, the use of synthetic fibres, which are endowed with remarkable properties in other respects, would be desirable.

Many processes have therefore been proposed for modifying the configuration of these filaments so that they can be employed in the preparation of woven and knitted articles whose aesthetic characteristics, elastic properties and insulating capacity are at least as satisfactory as those of natural fabrics.

The processes at present most commonly employed consist in imparting to the already formed yarn temporary deformations which are then set, generally by heat treatment. These processes generally have the disadvantage that they cannot be carried out continuously with the production of yarn: they involve therefore intermediate manipulations such as copping and winding, which increase the cost of the textured yarns obtained. In any case, they constitute an additional stage and lengthen the process of production.

Other processes utilise, for modifying the appearance of the filaments, a structural heterogeneity in the crosssection of these filaments. These heterogeneities, which may be of various natures, create internal stresses which produce undulations when they are relieved.

For example, each filament may comprise two or more chemically different constituents disposed side by side and having different shrinkage properties. Thus, it is possible to extrude through the same spinneret hole a polyamide and a polyester, or two different polyamides, and so to obtain composite filaments formed of two constituents.

For preparing such filaments, the various constituents are separately melted in separating melting devices and separately fed to the spinneret from which they are extruded side by side.

3,408,277 Patented Oct. 29, 1968 "ice The filaments may also be made of a single polymer, in which the heterogeneity which produces the crimping is of a physical nature. This type of filament can be obtained, for example, by asymmetrically cooling, downstream of the spinneret, filaments prepared by melt extrusion. Already formed filaments may also be rendered non-homogeneous, more especially by passing them over a heated knife-edge or by treating them with a swelling agent.

It is furthermore possible to prepare filaments directly by extrusion, using the same process as for filaments having chemically different constituents, the various melting devices being supplied with chemically identical polymers which, however, have different characteristics, such as viscosity or molecular weight. These polymers can be made separately or obtained from a single source polymer by pretreating it under different conditions.

The present invention provides a process for the preparation of spontaneously crimpable composite filaments by simultaneous extrusion through the same spinneret hole of at least two chemically identical constituents having different characteristics, i.e. a process of the last of the various types described above.

The process consists in continuously melting a thermoplastic linear polymer, of which at least one characteristic changes at elevated temperature, dividing the melt into at least two streams, subjecting these streams to different thermal treatments, and then extruding them contiguously in the form of continuous filaments.

This process is applicable more particularly to the preparation of composite filaments based on polypropylene, but it may also be used to prepare filaments generally from thermoplastic polymers which can be melt spun and of which at least one characteristic, such as viscosity or molecular weight, rapidly changes at elevated temperature, and notably at the temperatures currently employed in the course of the melt spinning of these polymers.

While filaments made by the process of the invention may comprise three or more constituents, filaments having two constituents are preferred since, as the number of constituents of the filament increases, the devices necessary for dividing the molten mass into a number of streams become increasingly cumbersome, and it is found more and more difficult to control the thermal treatments applied to these various streams.

Thus the melt will usually be divided into equal streams, but it might be divided into a larger number of streams, in which case the filaments will not consist of equal parts, but of strips of dissimilar cross-sections.

The heat treatments to which the various polymer streams are subjected may differ in various ways.

For example heat treatments of different durations but at the same temperature may be applied, eg the path traversed by one of the polymer streams may be longer than that traversed by the other before they join at the spinneret; or the heat treatments may be of identical duration, but at different temperatures; or finally thermal treatments of different duration and different temperature may be applied.

Which of these methods will be chosen in any particular case will depend on the polymer employed, the apparatus available etc. Whichever of these methods is employed the heat treatments will of course be of different intensities, in the sense that they will have different effects on the different polymer streams.

The process of the invention may be carried out in a spinning apparatus comprising essentially a continuously operating melting device provided with means for the supply of polymer, and with means for expelling molten polymer, at least two ducts communicating at one end with the outlet end of the melting device and at the other with a supply chamber of a spinneret, and adapted to cause polymer melt passing therethrough at the same rates of flow to be given different thermal treatments, a compartmented supply chamber, of which each compartment is connected to the outlet of a particular heating duct and communicates separately with the orifice or with some or all of the orifices of the spinneret. Such apparatus is also within the scope of the invention. The several ducts may, for example have different lengths or be provided with separately controllable heating means so that they can be heated to different temperatures or both. Advantageously each duct includes a metering pump near or at its input end.

One form of apparatus according to the invention is diagrammatically illustrated :by way of example in the accompanying drawing, in which the figure is a vertical cross-section of a spinning device.

Referring now to the drawing, the spinning device comprises a cylindrical melting chamber 2 which can be supplied with polymer through a hopper 1 and heated by means of elements 3. This chamber is provided with a central screw 4 driven by a motor (not shown), which conveys the polymer through the interior of the chamber. At its output end the chamber 2 communicates with two ducts 5 and 6 through two pumps 7 and 7 The two ducts are heated by elements 8 and 8' and are of different lengths. Each leads into one of the cells 9 of a filtration unit, and each cell communicates through a channel 13 with one compartment 10 of the supply chamber of a spinneret 11.

The filaments obtained by the spinning process of the invention may be crimped in various ways. Thus the crimp may be generated spontaneously immediately after a hot stretching operation carried out under the usual conditions for the type of filaments involved, or it may arise in the course of a subsequent heat treatment, such as steaming or treatment in boiling water, without applied tension.

The crimp obtained is of the helical typpe, and its intensity is a function of the difierence of the shrinkage properties of the constituents of the filaments, this difference being in turn dependent on the difference between the heat treatments undergone by the various polymer streams.

The crimped filaments thus obtained have high bulk under low tension and high elasticity. The crimp disappears under sufiiciently high tension, but returns spontaneously when the tension is removed. Thus subsequent application of high tension to the filaments, for example in the course of winding after stretching, does not substantially influence the crimp inherently present in the filaments.

Preferably, the conditions of the process are so adjusted that the filaments obtained have a degree of crimp above 150.

By degree of crimp is meant the ratio L-Lo L )XlOO Example 1 An apparatus of the type illustrated in the drawing is supplied with polypropylene having a viscosity index in the molten state of 0.6.

This polymer is melted in the chamber 2 and reaches .at its outlet end 12 a temperature of 285 C. It then divides into two streams, which are taken up by the pumps 7, 7', and enter the ducts and 6, which are maintained at a temperature of 310 C. The length of 4 the duct 6 is three times the length of the duct 5 having a capacity of 13 cc.

The two streams of polymer are extruded through the spinneret 11 to give twelve composite filaments which are wound up at 600 metres per minute. A 273 denier yarn is obtained and is stretched at a rate of 200 metres per minute by a factor of 5, over a pin at C. and a plate at C. to give a yarn having a tenacity of 5.38 g. per denier and an elongation of 31.4%. The yarn as obtained on the bobbin possesses a smooth appearance, but if it is unwound under low tension it acquires a very high bulk owing to the spontaneous crimping of the composite filaments. After treatment in boiling water for 10 minutes, this yarn has a degree of crimp of 359.

Example 2 Using the same apparatus and polymer as in Example 1, a number of runs are made, in each of which the temperature maintained in the ducts 5 and 6 is varied, all other conditions remaining the same. In each run, a spinning speed of 600 metres per minute is employed, and the yarns obtained are stretched by a factor of 5 at 200 metres per minute over a pin at 90 C. and a plate at 130 C.

The degree of crimp is measured on the crimped filaments obtained by unwinding under a low tension, and the following results are obtained:

Temperature in Degree of the ducts crimp 310 C. 359 300 C. 277 280 C. 17.6

Example 3 This example shows that the temperature and the ratio of the durations of the heat treatments are not the only variables which may be adjusted in order to vary the degree of crimp, but that the absolute values of these durations also has an effect.

In carrying out these runs, an apparatus of the same type as before was employed, the duct 6 being three times as long as the duct 5 having a capacity of 13 cc.

A polypropylene having a viscosity in the molten state of 0.6 is again employed; the spinning speed is 600 metres per minute, and the drawing factor 4.

The following results are obtained:

Temperature in Total rate of Degree of the ducts, deg. supply of polycrimp Iner, g-lmin.

We claim:

1. A process for the production of spontaneously crirnpable composite filaments which comprises continuously melting in a common melting device a thermoplastic linear polymer having shrinkage properties which change at elevated temperature, dividing the resulting melt into at least two streams, subjecting each stream to a different thermal treatment at elevated temperature to give the streams different physical properties, merging said streams, and spinning the streams to form at least one composite filament.

2. Process according to claim 1 in which the melt is divided into two streams.

3. Process according to claim 1 in which the streams are given thermal treatments of different durations.

4. Process according to claim 1 in which the streams are given thermal treatments at different temperatures.

5. Process according to claim 1 in which the thermoplastic polymer is polypropylene.

6. Apparatus for the production of composite filaments comprising a continuously operable melting device provided with means for the supply of polymer and means for discharging molten polymer therefrom, a compartmented spinneret supply chamber having a plurality of separate compartments for spinning bicomponent filaments, means including at least two ducts to cause polymer melts passing from said melting device to said supply chamber to give the melts different thermal treatments, said ducts each communicating at one end with the discharge end of said melting device and at the other end with a respective compartment of said supply chamber, and each of said compartments having an outlet communicating with at least one spinneret orifice.

7. Apparatus according to claim 6 in which said ducts difier in length.

8. Apparatus according to claim 6 in which said ducts are provided with separately controllable heating means.

9. Apparatus according to claim 6 in which each duct is provided with a metering pump near its input end.

10. A process for the production of crimped filaments, which comprises continuously melting in a common melting device a thermoplastic linear polymer having shrinkage properties which change at elevated temperature, dividing the resulting melt into at least two streams, subjecting each stream to a different thermal treatment at elevated temperature to give the streams different physical properties, merging said streams, extruding the streams to form at least one composite filament, and heating said filament to a temperature at which crimp develops spontaneously.

11. A process according to claim 10, in which said filament is in the form of a multi-filament yarn.

References Cited UNITED STATES PATENTS 3,200,440 8/1965 Bryan et al. 264-171 X FOREIGN PATENTS 979,083 1/1965 Great Britain. 1,342,403 9/ 1963 France.

JAMES A. SEIDLECK, Primary Examiner.

20 I. H. WOO, Assistant Examiner. 

